For decades, cytomorphological analysis of cytospin preparations of cerebrospinal fluid (CSF) has been considered the gold standard for the diagnosis of leptomeningeal involvement in both primary and secondary central nervous system lymphomas. In addition, it contributes to the diagnosis of other hematological and non-hematological tumors that are localized in the central nervous system (CNS). Although such conventional cytological analyses of CSF are associated with a high specificity for identification of CNS disease in lymphoma and other cancer patients, evidence has also accumulated about its limited sensitivity with a frequency of between 20% and 60% false negative results (Chamberlain et al, Sem Oncol 2009; 36: s35-s45). More recently, multiple studies have shown that flow cytometry immunophenotyping of cells present in CSF samples provides a similarly specific but much more sensitive approach for the detection of leptomeningeal disease in aggressive B-cell non-Hodgkin lymphomas (B-NHL) and in other lymphoid and myeloid malignancies, as well as in solid tumors (Subira et al HIV Med 2005, 6: 21-26; Quijano et al J Clin Oncol, 2009; 27: 1462-I 469;.Bromberg et al J Neurology 2007; 68: 1674-1679; Hedge et al Blood 2005, 105: 496-502). Among lymphoma cases, such increased sensitivity is associated with a dismal patient outcome due to increased CNS and systemic relapse rates (Hedge et al, Blood 2005, 105: 496-502; Sancho et al, Eur J Haematol 2010). Despite the increased sensitivity of multiparameter flow cytometry versus conventional cytological procedures, still a significant proportion of patients who show no neoplastic B-cells or other tumor cells in their CSF, either by flow cytometry or by conventional cytology, display neurological symptoms highly suspicious of CNS involvement by the lymphoma or other type of tumor with or without results compatible with a diagnosis of tumor involvement of the CNS by magnetic resonance imaging (MRI) and other imaging techniques. In parallel, still a significant fraction of all CNS relapses that occur among e.g. aggressive B-NHL involve patients who showed flow cytometry negative (FCM-)/conventional cytology (CC-) CSF. Altogether, these results point out the need for more sensitive approaches to detect CNS involvement among aggressive B-NHL and also other hematological and non-hematological tumors.
In this regard, it has been suggested that in such cases, false negative results of FCM and CC could be due to occurrence of parenchymal infiltration by the tumor cells, in the absence of leptomeningeal involvement. Although, definitive demonstration of this hypothesis still remains to be established, it could be speculated that while in cases showing leptomeningeal involvement, lymphoma cells could easily and rapidly reach CSF allowing their detection by FCM and/or CC, in cases where CNS involvement is restricted to parenchymal localizations, tumor cells would not easily spread to the cerebroespinal fluid (or the vitrous fluid). However, under such circumstances it would be expected that due to an increased cellular turn-over, an increased release of soluble tumor cell proteins, RNA, DNA and other cell components by living or dying tumor cells, could make their levels into the CSF (and/or the vitrous fluid) detectable. In fact, a few studies have been previously reported in which the amount of specific cellular immune response-associated (but not tumor related) proteins, e.g., CD27 (Kersten et al, Blood 1996, 87: 1985-1989; Murase et al, Cancer Lett 1998, 132: 181-186), free light chains (Hildebrandt et al BMC cancer, 2007, 7: 185; Schroers et al Eur J Haematol 2010, 85: 236-242) and antithrombin (Roy et al, J Clin Oncol 2008, 26: 96-105) are detected in CSF from patients with multiple CNS diseases, despite such measurements, provided diagnostically inefficient results. Of note, none of these proteins are tumor-specific and they could not be directly linked with tumor cell death and/or active secretion by tumor cells.